We are studying the mechanism of regulation in skeletal and smooth muscle. In skeletal muscle our efforts are directed towards understanding the role played by tropomyosin. In particular we wish to develop a biochemical method to determine whether tropomyosin moves relative to actin during the contraction-relaxation cycle. Our approach has been to study the extent of fluorescent energy tranfer between two suitable chromophores, one on tropomyosin and the other on actin. This effect is very sensitive to the distance separating the donor and acceptor molecules and thus should be suitable to detect any relative movement. Initial experiments indicate that tropomyosin does move, and now we must investigate whether or not this movement is an essential feature of the regulatory mechanism, or merely an associated process. In smooth muscle (gizzard and arteries) our knowledge is at a much more fundamental level, and we are primarily concerned with establishing the proteins that are involved in the regulatory mechanism. Our studies suggest that a troponin-like protein is not present and that regulation is the function of the myosin molecule. There are, however, indications that additional factor(s) could be involved and we are trying to identify these. BIBLIOGRAPHIC REFERENCES: S. Driska and D.J. Hartshorne. "The contractile proteins of smooth muscle. Properties and components of a Ca2 ion-sensitive actomyosin from chicken gizzard". Arch. Biochem. Biophys. 167:203-213 (1975). D.J. Hartshorne, L. Abrams, M. Aksoy, R. Dabrowska, S. Driska, and E. Sharkey. "Molecular basis for the regulation of smooth muscle actomyosin". In "Biochemistry of smooth Muscle". Ed. N. Stephens, 1975. University Park Press, Baltimore.